1. Field of the Invention
The present invention relates to an electromagnetic field measuring method for measuring axially symmetric electromagnetic fields generated by an electromagnetic lens, or the like, employed in electron beam exposure units or electron microscopes.
2. Description of the Related Art
Electron microscopes have been widely adopted as a means for observing submicroscopic objects. A scanning type electron microscope (SEM) has been used as a typical electron microscope. The scanning type electron microscope scans a sample with an electron beam that is converged to a very small spot, and detects electrons transmitted or reflected by the sample. The resolution is determined with the size of the spot of the irradiated electron beam.
Moreover, electron beam exposure units have attracted attention because of their capability as lithographic units for exposing submicroscopic patterns including patterns that define semiconductor devices. The electron beam exposure unit exposes, like the scanning type electron microscope, a resist applied to a substrate to an electron beam converged on a very small spot so as to pattern the resist. The electron beam exposure unit is characterized by its ability to offer a higher resolution than the one offered by lithography and to therefore draw finer patterns. The resolution that can be offered by the electron beam exposure unit is determined by the size of the spot of the irradiated electron beam.
In the electron microscope or electron beam exposure unit, for converging or deflecting an electron beam, electric fields or magnetic fields are utilized and an electronic lens or magnetic lens is employed. The magnetic lens produces a magnetic field when current flows into a wire wound coil. The magnetic lens is used as a convergent lens for converging an electronic beam or as a focusing coil for changing a focal point. Almost all the magnetic lenses are intended to generate axially symmetric magnetic fields, and they are manufactured by creating a coil, using a closely wound wire, so that an exactly axially symmetric magnetic field can be generated. Many other apparatuses are employed which generate magnetic fields. For example, there is a magnetic resonance imaging computed tomography modality utilizing nuclear magnetic resonance. Almost all the apparatuses generate an exactly axially symmetric magnetic field. Moreover, an electrostatic lens for generating an axially symmetric electric field is employed in television sets. Hereinafter, a magnetic field generator for generating axially symmetric magnetic fields will be described as an example. The same will apply to an electric field generator for generating an axially symmetric electric field. The present invention can be adapted to the electric field generator.
For manufacturing or developing magnetic field generators for generating axially symmetric magnetic fields, it is necessary to measure magnetic fields generated by the generators to see if they have the desired strengths. According to a magnetic field measuring method of a prior art, a three-dimensional moving mechanism is used to move a measuring probe of a gaussmeter. A range within which the measuring probe can be moved is limited by the three-dimensional moving mechanism. There is a problem in that this kind of three-dimensional moving mechanism is expensive. In particular, for measuring magnetic fields induced on the whole circumference of a magnetic field generator, a three-dimensional moving mechanism having an arm-shaped movable carriage must be employed. This kind of three-dimensional moving mechanism is very large and quite expensive.
Moreover, for improving precision in measurement, it is necessary to improve the accuracy of a position to which the measuring probe is moved. For this purpose, a high-precision three-dimensional moving mechanism must be employed. This also results in making the three-dimensional moving mechanism expensive.
Furthermore, when measurement data acquired by moving the measuring probe is processed, an axis of symmetry of a magnetic field is calculated from the measurement data. The number of operations needed for this processing is so large that it is hard to identify the axis of symmetry precisely.
Moreover, when the magnetic field generator is incorporated in the electron beam exposure unit, the magnetic field generator is positioned in reference to the contour thereof, or in other words, in reference to a mechanical axis of symmetry. A positional deviation between the mechanical axis of symmetry of the magnetic field generator and the axis of symmetry of a magnetic field is measured. The magnetic field generator must then be incorporated after the position thereof is corrected to compensate for the positional deviation. However, there is a problem in that measuring the positional deviation between the mechanical axis of symmetry and the axis of symmetry of a magnetic field is difficult and expensive work. This is because a measuring unit similar to a three-dimensional measuring instrument must be used to measure the magnetic field generator and the position of the measuring probe.
As described above, the measuring method of the prior art for measuring axially symmetric magnetic fields is difficult and expensive work.